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Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil

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Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil. / Koyama, Daisuke; Milner, Matthew; Orr-Ewing, Andrew.

In: Journal of Physical Chemistry B, Vol. 121, No. 39, 05.10.2017, p. 9274-9280.

Research output: Contribution to journalArticle

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Koyama, D, Milner, M & Orr-Ewing, A 2017, 'Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil', Journal of Physical Chemistry B, vol. 121, no. 39, pp. 9274-9280. https://doi.org/10.1021/acs.jpcb.7b06917

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Koyama, Daisuke ; Milner, Matthew ; Orr-Ewing, Andrew. / Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil. In: Journal of Physical Chemistry B. 2017 ; Vol. 121, No. 39. pp. 9274-9280.

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@article{df2134f9d98b4d2b9916fd7398696294,
title = "Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil",
abstract = "The computationally predicted presence of two structurally distinct minima in the first triplet excited (T1) state of 2-thiouracil (2TU) is substantiated by sub-picosecond transient vibrational absorption spectroscopy (TVAS) in deuterated acetonitrile solution. Following 300-nm ultraviolet excitation to the second singlet excited state of 2TU, a transient infrared absorption band centered at 1643 cm-1 is observed within our minimum time resolution of 0.3 ps. It is assigned either to 2TU molecules in the S1 state, or to vibrationally hot T1 state molecules, with the latter assignment more consistent with recent computational and experimental studies. The 1643 cm-1 band decays with a time constant of 7.2 ± 0.8 ps, and there is corresponding growth of several further bands centered at 1234, 1410, 1424, 1443, 1511, 1626 and 1660 cm-1 which show no decline in intensity over the 1 ns time limit of our measurements. These spectral features are assigned to two different conformations of 2TU, corresponding to separate energy minima on the T1 state potential energy surface, on the basis of their extended lifetimes, computed infra-red frequencies, and the observed quenching of the bands by addition of styrene. Corresponding measurements for the 4-thiouracil (4TU) isomer show sub-picosecond population of the T1 state, which vibrationally cools with a time constant of 5.2 ± 0.6 ps. However, TVAS measurements in the carbonyl stretching region do not distinguish the two computed T1-state conformers of 4TU because of the similarity of their vibrational frequencies.",
author = "Daisuke Koyama and Matthew Milner and Andrew Orr-Ewing",
year = "2017",
month = "10",
day = "5",
doi = "10.1021/acs.jpcb.7b06917",
language = "English",
volume = "121",
pages = "9274--9280",
journal = "Journal of Physical Chemistry B",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "39",

}

RIS - suitable for import to EndNote

TY - JOUR

T1 - Evidence for a Double Well in the First Triplet Excited State of 2-Thiouracil

AU - Koyama, Daisuke

AU - Milner, Matthew

AU - Orr-Ewing, Andrew

PY - 2017/10/5

Y1 - 2017/10/5

N2 - The computationally predicted presence of two structurally distinct minima in the first triplet excited (T1) state of 2-thiouracil (2TU) is substantiated by sub-picosecond transient vibrational absorption spectroscopy (TVAS) in deuterated acetonitrile solution. Following 300-nm ultraviolet excitation to the second singlet excited state of 2TU, a transient infrared absorption band centered at 1643 cm-1 is observed within our minimum time resolution of 0.3 ps. It is assigned either to 2TU molecules in the S1 state, or to vibrationally hot T1 state molecules, with the latter assignment more consistent with recent computational and experimental studies. The 1643 cm-1 band decays with a time constant of 7.2 ± 0.8 ps, and there is corresponding growth of several further bands centered at 1234, 1410, 1424, 1443, 1511, 1626 and 1660 cm-1 which show no decline in intensity over the 1 ns time limit of our measurements. These spectral features are assigned to two different conformations of 2TU, corresponding to separate energy minima on the T1 state potential energy surface, on the basis of their extended lifetimes, computed infra-red frequencies, and the observed quenching of the bands by addition of styrene. Corresponding measurements for the 4-thiouracil (4TU) isomer show sub-picosecond population of the T1 state, which vibrationally cools with a time constant of 5.2 ± 0.6 ps. However, TVAS measurements in the carbonyl stretching region do not distinguish the two computed T1-state conformers of 4TU because of the similarity of their vibrational frequencies.

AB - The computationally predicted presence of two structurally distinct minima in the first triplet excited (T1) state of 2-thiouracil (2TU) is substantiated by sub-picosecond transient vibrational absorption spectroscopy (TVAS) in deuterated acetonitrile solution. Following 300-nm ultraviolet excitation to the second singlet excited state of 2TU, a transient infrared absorption band centered at 1643 cm-1 is observed within our minimum time resolution of 0.3 ps. It is assigned either to 2TU molecules in the S1 state, or to vibrationally hot T1 state molecules, with the latter assignment more consistent with recent computational and experimental studies. The 1643 cm-1 band decays with a time constant of 7.2 ± 0.8 ps, and there is corresponding growth of several further bands centered at 1234, 1410, 1424, 1443, 1511, 1626 and 1660 cm-1 which show no decline in intensity over the 1 ns time limit of our measurements. These spectral features are assigned to two different conformations of 2TU, corresponding to separate energy minima on the T1 state potential energy surface, on the basis of their extended lifetimes, computed infra-red frequencies, and the observed quenching of the bands by addition of styrene. Corresponding measurements for the 4-thiouracil (4TU) isomer show sub-picosecond population of the T1 state, which vibrationally cools with a time constant of 5.2 ± 0.6 ps. However, TVAS measurements in the carbonyl stretching region do not distinguish the two computed T1-state conformers of 4TU because of the similarity of their vibrational frequencies.

U2 - 10.1021/acs.jpcb.7b06917

DO - 10.1021/acs.jpcb.7b06917

M3 - Article

C2 - 28895733

VL - 121

SP - 9274

EP - 9280

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 39

ER -